A 30-year-old man is in critical condition after police say he was beaten unconscious with a baseball bat in his east Boulder apartment late Monday night.

Officers were dispatched just before midnight Monday to an apartment in the 5600 block of Arapahoe Avenue on reports that a man had been assaulted with a baseball bat, according to a Boulder police news release.

Upon arrival, officers found Aaron Matthew Tuneberg, 30, unconscious inside his apartment, suffering from serious head and other injuries, according to police. He was transported to an area hospital by ambulance and remains in critical condition.

Police were alerted to the apparent assault by 18-year-old Luke Jonah Pelham, who told dispatchers at the time he had been visiting Tuneberg to pick up an item Tuneberg had borrowed from a mutual friend. Pelham told police that he was leaving Tuneberg's apartment when he saw another man on the stairs carrying a bat. He said he later heard sounds that led him to believe someone was being beaten with a bat.

Pelham called police about an hour after the reported encounter, after he had walked home, according to the news release.

Investigators, after trying unsuccessfully to track the suspect with a canine unit, eventually found evidence in a nearby parking lot they believed was connected to the assault and determined that the victim knew who attacked him.

The information led police at 4:20 a.m. Tuesday to arrest Austin Holford, 18, who was found sleeping in a van parked in a lot near 30th Street and Iris Avenue.

They also arrested Pelham in connection with the assault. He turned himself in voluntarily, police say.

Both were arrested on suspicion of first-degree assault and first-degree burglary, according to police.

Anyone with additional information about the incident is asked to contact Crime Stoppers at 800-222-8477 or www.crimeshurt.com.